Walvoil SD5/2-P(KG3-175)/18L/18LAET is a 2 spool hydraulic control valve and manual hydraulic monoblock valve designed for directional flow control in mobile and industrial hydraulic systems up to 315 bar and 45 L/min.

　　Product Type Definition

　　A monoblock directional control valve is a single-cast hydraulic component containing all internal channels and spool bores within one solid body,eliminating inter-section seals and potential leak paths present in sectional valves.This product category typically includes manual,hydraulic,and electro-hydraulic actuation variants,with classification based on spool count(1 to 7 sections),circuit configuration(parallel,series,or tandem),and control type.The Walvoil SD5/2-P falls into the medium-flow manual monoblock segment,engineered for open and closed center hydraulic systems requiring two independent actuator control functions.

　　Key Specifications

　　Rated flow:45 L/min(12 US gpm)

　　Max operating pressure(parallel/tandem circuit):315 bar(4,600 psi)

　　Max operating pressure(series circuit):250 bar(3,600 psi)

　　Max return line pressure(T port):25 bar

　　Number of spools/sections:2

　　Spool stroke:37 mm

　　Plunger diameter:16 mm

　　Port thread:G 3/8”BSP(ISO 228/1)

　　Port functions:P(pressure),A/B(work ports),T(tank return)

　　Circuit type:Parallel with main relief valve and load check valve in P-channel

　　Control type:Manual mechanical lever

　　Ambient temperature range:-20°C to+80°C

　　Sealing material:Nitrile rubber(NBR)

　　Internal leakage(max per spool):3 cm³/min

　　Pitch between sections:37 mm

　　Construction:Monoblock cast iron body

　　Technical Highlights

　　Integrated main pressure relief valve and load check valve in the P-channel.This built-in configuration ensures each actuator receives flow from the pump without pressure loss from other simultaneously operated sections,reducing energy waste and improving multi-function coordination.

　　High internal tightness maintained at full rated flow.For applications requiring precise spool metering at 45 L/min,the valve limits internal cross-port leakage to 3 cm³/min per spool under rated conditions,minimizing actuator drift and improving positional accuracy.

　　Heavy-duty monoblock casting eliminates inter-section leak points.Unlike sectional valves where tie rod torque and gasket integrity create ongoing maintenance concerns,the SD5’s single-body construction provides inherent leak resistance and reduces total ownership cost over the valve’s service life.

　　Operating temperature range of-20°C to+80°C covers most outdoor mobile equipment conditions.Performance specifications are validated with mineral oil of 46 mm²/s(46 cSt)viscosity at 40°C,providing a reference baseline for system designers to calculate viscosity effects at extreme temperatures.

　　Applications

　　Metallurgical hydraulic systems:Provides reliable flow control for furnace door actuators and material handling cylinders in steel mill environments where dust and high ambient temperatures(up to 80°C)are present,with monoblock construction reducing contamination ingress points.

　　Marine hydraulic systems:Controls winch drives,hatch actuators,and steering gear cylinders on vessels,where G 3/8”BSP ports allow compatibility with marine-standard fittings and the cast iron body offers corrosion resistance in salt-air environments.

　　Construction and earth-moving equipment:Enables precise boom and bucket control on small front loaders,backhoes,and compact excavators,with parallel circuit design allowing simultaneous or independent cylinder actuation without flow starvation.

　　Agricultural machinery and material handling:Regulates hydraulic functions on telehandlers,balers,and conveyors,where manual lever control provides operators with direct tactile feedback essential for fine positioning tasks.

　　Mobile hydraulic equipment:Serves as the directional control unit for orbital motors,radial piston motors,and cylinder circuits on aerial work platforms and truck-mounted cranes,handling intermittent duty cycles up to 315 bar peak pressure.

　　Selection Guidance

　　Suitable for:Open center or closed center hydraulic systems requiring two independently controlled actuator functions with flow requirements between 20 L/min and 45 L/min and operating pressures up to 315 bar.

　　Suitable for:Applications where compact envelope and weight reduction are priorities,as monoblock construction is significantly lighter and more space-efficient than equivalent sectional valves.

　　Suitable for:Systems using G 3/8”BSP porting standards with mineral oil-based hydraulic fluids operating within-20°C to+80°C ambient range.For low-temperature operation below-20°C,consider alternative sealing materials as NBR seals may harden and increase leakage.

　　Not recommended for:Systems requiring more than 2 spools.The SD5/2-P is a fixed two-section valve;applications needing 3 or more functions should consider SD5 variants with up to 7 sections or sectional valve configurations.

　　Not recommended for:High-cycle continuous operation above 315 bar.For applications with sustained pressure exceeding 315 bar or flows above 45 L/min,a larger platform such as Walvoil SD6 or SD8 series(higher flow capacity)or a sectional valve(broader pressure/flow range)should be evaluated.

　　FAQ

　　1.What is the maximum operating pressure for this valve in parallel circuit configuration?

　　315 bar(4,600 psi).The same pressure rating applies to tandem circuit configurations,while series circuit operation is limited to 250 bar(3,600 psi)per manufacturer specifications.

　　2.Does the SD5/2-P support simultaneous operation of both spools?

　　Yes,the parallel circuit design allows both spools to operate simultaneously.However,total flow demand from both actuators should not exceed the pump’s rated supply flow,as the valve does not incorporate flow sharing priority logic.

　　3.What is the maximum return line pressure allowed at the T port?

　　25 bar.Exceeding this back pressure may cause excessive spool friction,increased internal leakage,or damage to the load check valve sealing elements.

　　4.How does this monoblock valve compare to a sectional valve for two-spool applications?

　　The monoblock SD5 is more compact,lighter,and lower cost than a two-section sectional valve,with fewer external leak points.However,if a spool or internal passage is damaged,the entire monoblock must be replaced rather than servicing an individual section.

　　5.What fluid viscosity range is recommended for proper valve operation?

　　Performance data is measured with mineral oil of 46 mm²/s(46 cSt)at 40°C.The valve operates reliably with viscosities from 15 cSt to 100 cSt at operating temperature;higher viscosities may increase pressure drop,while lower viscosities may increase internal leakage beyond the 3 cm³/min specification.